The present invention relates to a radiation tomography method and apparatus, and more particularly, to a radiation tomography method and apparatus which can produce a tomographic image based on a projection image of a subject in a plurality of view directions using a radiation beam having an extent and a thickness.
Radiation tomography apparatuses include the x-ray CT (computed tomography) apparatus, for example. In the x-ray CT apparatus, x-rays are employed as radiation. The apparatus scans a subject by a radiation emission/detection system rotating around the subject to measure x-ray projection data of the subject in a plurality of view directions around the subject, and produces (i.e., reconstructs) a tomographic image based on the projection data.
The radiation emission system has an extent which encompasses the imaging range, and emits an x-ray beam which has a predetermined thickness in the direction orthogonal to the extent. The radiation detection system detects the projection data by a multi-channel detector in which multiple x-ray detectors are arranged in an array in the extent direction of the x-ray beam.
The thickness of the x-ray beam determines the slice thickness for tomography. The slice thickness is set to an appropriate value according to the purpose of tomography. To set the slice thickness, a collimator or the like to regulate the thickness of the x-ray beam is used. Even if radiation other than x-rays, such as .gamma.-rays is employed, the thickness of a radiation beam, i.e., the slice thickness is regulated also by the collimator or the like.
In the case of pulmonary cancer examination, for example, a multi-slice scan with a relatively thick slice is carried out to efficiently and contiguously image the entire lung field with a limited number of slices. In addition, a multi-slice scan with a thin slice is carried out to obtain an image having good detail definition. However, since the number of slices is limited, the multi-slice scan with a thin slice is performed on the slices lying at intervals.
The set slice thickness is maintained throughout the imaging of a sequence of tomographic images. Accordingly, when the multi-slice scanning is performed as described above, a contiguous scan for the entire lung field with a thick slice is first carried out, and then the slice thickness must be reset by the collimator or the like to restart another multi-scan with a thin slice. This procedure is poor in efficiency.